Vehicles have long implemented glass to enclose a cabin of the vehicle while still allowing visibility for the driver of the vehicle. The glass is typically disposed on an angle to enclose the cabin. Automotive glass is typically either a tempered (or toughened) glass or a laminated glass which is produced by bonding two or more panes of glass together with a plastic interlayer. The characteristics of glass such as automotive glass, and the angled disposition of this glass when applied as a window of a vehicle, provide challenges to the effective integration of an antenna with the window of the vehicle. Automotive manufacturers have strict requirements as to the amount of visual obstruction caused by antennas integrated with windows of the vehicle. As is known in the art, one of the more stringent requirements is that a footprint of an antenna disposed on glass must not limit the driver's visibility or visually block an area larger than approximately 100 mm×100 mm. Some vehicle designs utilize black ceramics along the periphery of the window of the vehicle. In this case, when the antenna is also placed on the periphery of the window, the antenna pattern is less visible to the driver. However, this placement limits the placement flexibility and potentially the performance of the antenna.
This integration of the antenna with the window improves aerodynamic performance of the vehicle and presents the vehicle with an aesthetically-pleasing, streamlined appearance. Integration of antennas for receiving RF signals, such as those generated by AM/FM terrestrial broadcast stations, has been a principal focus of the industry. However, to meet customer demand for wireless communication applications in the vehicle, the focus is expanding to integrating antennas for transmitting and/or receiving RF signals in cellular frequency bands.
Currently, there are several wireless communication applications that utilize different cellular frequency bands. For example, two cellular frequency bands utilized in North America are the Advanced Mobile Phone Service (AMPS), ranging from 824-894 MHz and the Personal Communication Service (PCS), ranging from 1850-1990 MHz. To have compatibility with these wireless communication applications, the vehicle may have multiple antennas. Multiple antennas enable the vehicle to transmit and/or receive signals in each of the different cellular frequency bands.
Various antennas for transmitting and/or receiving RF signals in the cellular frequency bands are well known in the art. Several of these antenna types are non-conformal when applied to a window (e.g. a whip, mast, or patch). An example of such an antenna is disclosed in the U.S. Pat. No. 6,429,819 (the '819 patent) to Bishop et al. The '819 patent discloses an antenna disposed on one side of a dielectric substrate, such as a printed circuit board, that includes a first antenna element and a second antenna element. A ground plane is disposed substantially parallel to and spaced from the first and second antenna elements. The first antenna element is a conductive patch having a rectangular shape measuring 127 mm×127 mm. The second antenna element includes two radiating elements defined as a slot within the first antenna element and arranged to form a bowtie shape. Additionally, the antenna of the '819 patent includes backside antenna elements located within a perimeter of the second antenna element and disposed on the opposite side of the dielectric substrate. The first antenna element provides a resonance at a first cellular frequency band, ranging from 880-960 MHz, and the second antenna element and the backside antenna elements provide a resonance at a second cellular frequency band, ranging from 1920-2170 MHz.
Notably, because the antenna of the '819 patent has antenna elements disposed on both sides of the dielectric, there are manufacturing challenges when integrating such a design on automotive glass such as tempered glass. For example, a radome may be needed to protect the first antenna elements and the ground plane or backside antenna elements from exposure to moisture, wind, dust, etc. that are present outside of the vehicle. Additionally, the antenna of the '819 patent has a larger footprint than desired by the automotive manufacturers to be integrated with automotive glass.
Therefore, it would be desirable to develop an improved antenna integrated with the window of the vehicle that is capable of transmitting and/or receiving RF signals in each of the different cellular frequency bands demanded by the wireless communication applications. Additionally, there remains an opportunity for a high-performing antenna that, when integrated with an automotive window, does not create a substantial visual obstruction nor alter the aesthetic appearance of the vehicle yet still maintains optimal reception.